//定位居中
.self-center(@type:absolute){
position:@type;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
}
//填充满父原素
.self-filled(@type:absolute){
    position: @type;
    left: 0;
    top:0;
    width: 100%;
    height: 100%;
}